This application relates to a tire pressure monitoring system wherein the count rate for determining a failed sensor is adjusted as a vehicle moves from a stationary state to a moving state.
Tire pressure monitoring systems are becoming widely utilized in modern vehicles. Typically, sensors are mounted within each of the tires and sense the pressure within the tire. The sensor has a transmitter to communicate through a wireless link, typically an RF link, with a control on the vehicle. The control is able to display any tire that has a low pressure condition to the vehicle operator.
These systems increase the safety of vehicle operation by reducing the number of vehicles operating with improperly inflated tires. However, many design challenges are raised in the implementation of these systems. One major challenge is monitoring whether the transmitters and sensors are operational. Thus, the control typically looks for expected transmissions from each of the sensors. The sensors are typically expected to transmit pressure information on some periodic basis. The counter counts the number of times a particular transmitter has failed to report when expected. Many conditions can result in a failure to report occasionally. Thus, the systems have a particular limit of failures to report before a transmitter is identified as failed.
Tire pressure monitoring systems are somewhat more reliable in their reporting when the vehicle is moving. When the vehicle is moving, there are fewer potentially interfering foreign bodies continuously adjacent to the vehicle. On the other hand, when a vehicle is parked, other vehicles may be parked nearby and other foreign objects may also be near the vehicle. For many reasons, the presence of such objects will sometimes reduce the ability of the control to properly receive a signal from the tire pressure transmitters.
Thus, it has been proposed that a higher failed transmitter count rate be utilized for a non-moving vehicle than the count rate utilized for a moving vehicle. Thus, in one case, if a vehicle is moving, 20 sequential missed messages may set the limit for the identification of a failed transmitter. However, when the vehicle is stationary, 72 missed messages may be the count limit. Obviously, other numbers would come within the scope of this invention.
Problems still exist with this basic format, however, in that the prior art has not successfully considered what may occur in the transition between a stationary vehicle to a moving vehicle due to the two different count limits.
In a disclosed embodiment of this invention, a method and control for a tire pressure monitoring system count the number of failures to transmit. If the vehicle is moving below a predetermined speed for a predetermined amount of time, then a higher xe2x80x9cstationary vehiclexe2x80x9d limit is utilized and compared to the count. On the other hand, while the vehicle is moving more quickly, a lower xe2x80x9cmoving vehiclexe2x80x9d limit is compared to the count.
The determination that a vehicle is stationary typically requires the vehicle to be moving below a particular rate of speed (i.e., 20 miles per hour) for a particular period of time. While the particular period of time may be 0 minutes, typically such systems require the vehicle to be below the speed limit for a period of time to eliminate the determination the vehicle is stationary, and should move into stationary mode, when the vehicle may be simply stopped at a stop sign, or in traffic. Thus, it is often the case that the vehicle will not move into the xe2x80x9cstationary vehiclexe2x80x9d mode until it has been below the rate of speed for several minutes.
In the present invention, if a determination is made that a vehicle which had been in xe2x80x9cstationary vehiclexe2x80x9d mode has returned to the xe2x80x9cmoving vehiclexe2x80x9d mode, then the number of failed transmitter counts may be reset. In a preferred embodiment, the system asks whether the count is between a lower limit and an upper limit. If so, then the count is reset to a number slightly below the lower limit. In this way, if a stationary vehicle has a transmitter with several failure to transmit occurrences in its count, the transmitter will not be immediately identified as having failed once the vehicle returns to a moving state. Moreover, in a most preferred embodiment the reset number and the number for triggering the reset may be slightly below the first limit as this would also allow for the transmitter to have a few expected cycles which could be missed even after the vehicle begins moving before the determination of a failed transmitter is made.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.